The present invention relates generally to the compacting of outer helical strands on a core having a relatively fixed diameter, and particularly to the compacting of cable or conductor in a manner that affords a number of advantages not presently available with the present state of the art.
Generally, apparatus employed to compact a stranded cable, i.e., a cable comprised of a plurality of individual wire strands, employs a solid stationary die to force an outer layer of the strands together on a core and into a compact cable structure in cross-section, as the cable and core are pulled through the die. More specifically, if a conductor comprised of seven strands is desired, six outer strands are compacted on a single wire, which wire comprises the core of the conductor, as the core wire and six outer strands are pulled through an appropriately sized die. If a nineteen-strand conductor is desired, the above seven-strand compacted conductor is employed as the core, and twelve outside strands are compacted on the seven strands, again with an appropriately sized die. In other words, whatever size (in diameter) cable is needed, each outside layer of strands is pulled throuh a die, with an appropriate core, and thereby compacted on the core. And each outside layer of strands enters the die from a rotating carriage carrying a corresponding plurality of spools of the wire strands, the rotating carriage causing the plurality of such strands to twist or rotate as they enter and pass through the die. It can be appreciated that lubrication of the annular, compacting surface of the die and the surfaces of the outer strands, which are in contact with the fixed die surface, is critical in such a process.
In addition, strands that are soft or annealed are difficult to compact in solid stationary dies, even with proper lubricants, as the metal of strands galls and chafes on the die surface. With hard, as-drawn wire, galling is not a substantial problem. In either case, when compacting with a die, pulling forces are exerted on the strands and the wire changes cross-sectional configuration and elongates. The metal, as it is being worked by the die, flows plastically and heat is generated from the cold work and friction between the fixed surface of the die and the outer strands. In such a state the strands are more susceptible to breakage by short duration, high tensile stress. Consequently, the softer or more annealed the strands are, or the smaller in diameter the strands are, the slower the speed must be to reduce wire breakage, yet the forces required to pull the cable through the dies remain substantial because of the fact that the die surfaces are fixed.
Another problem associated with stationary dies is the tendency of wire shapes that are other than round, such as trapezoidal, to rotate individually about their axes as they are pulled through the dies. Such a tendency locates the individual strands in the completed cable in a tilted or cocked manner such that the effective diameter of the cable is increased and the cross-section of the cable is not solidly packed.
Further, because of the friction and forces between the strands and fixed dies employed for cable compacting, a substantial amount of working of the strands takes place. If the metal of the strands is soft, the strands leaving the dies are work-hardened. If the strands to be compacted are already work-hardened, which occurs when the strands are drawn, the hardness of such strands is increased by the cold work encountered in compacting in fixed dies. In cases where stranded cables are produced for end uses in which workmen must be able to bend and otherwise manipulate the cable, such as with building wire, the strands of the cable should be soft. This requires a minimum of working in the stranding and compacting process.
U.S. Pat. No. 1,947,775 to Hill discloses the use of opposed rollers that provide a die opening employed to form a pre-spiralled non-circular (i.e., triangular) stranded conductor for a cable comprised of a plurality of such conductors. The rollers are rotated about the longitudinal axis of the conductor in the forming process, and the rollers are driven, along with a capstan positioned to pull the conductor through the rollers and opening, the power of the driving action being divided between the capstan and rollers to control tension on the conductor and thereby avoid stretching of the conductor in the rolling process.
A similar structure and process are disclosed in U.S. Pat. No. 2,128,777 to Hunter et al, except that two consecutive roller dies are employed to form a non-circular, sector or triangular shaped opening and conductor, the two roller dies again being operative to rotate or revolve about the axis of the conductor in the conductor forming process.
While the apparatus of these two patents reduces work-hardening and plastic flow problems associated with stationary dies, the rollers of the apparatus do not compact outer strands on a conductor core having a relatively fixed diameter, and in such a manner that insures that the stress pattern of the cable will be uniform through the cross-section of the cable. Rather, the function of the roller dies of Hill and Hunter et al is to form a spiralling, triangular or sector shaped conductor which requires revolving the rollers about the axis of the conductor, and driving the rollers in order to control tension on the conductor. The sectors are then placed together to form a composite cable.
In U.S. Pat. No. 1,979,013 to Rohs there is disclosed the use of rollers to preform individual wires with a twist that is shorter than the pitch required for the cable produced from the wires, see column 1, lines 31 to 38 and lines 49 to 54 of the patent. And like Hill and Hunter et al, the Rohs rollers are revolved about the axis of the wire conductor to form the pitch of the conductor.